# Pillow: TarIO negative size field causes infinite CPU-spin loop

Advisory record · `GHSA-3j72-p6qg-6xp7`

- **Identifiers:** `GHSA-3j72-p6qg-6xp7` · `BIT-pillow-2026-96642` · `CVE-2026-96642` · `PYSEC-2026-4341`
- **State:** Confirmed
- **Severity:** CVSS 7.1 High
- **Critical:** No
- **Weakness (CWE):** [CWE-835](https://cwe.mitre.org/data/definitions/835.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md)
- **Published:** 22 Oct 2026
- **Updated:** 29 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 22 Oct 2026, 16:01 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `pillow` (PyPI): affected `<13.0.0`; fixed in `13.0.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Pillow versions before 13.0.0 have a flaw in TarIO, the helper class that reads a member from a tar archive. It does not check that a tar header's size field is non-negative, so a crafted header with a negative size makes the reader seek back to where it started and loop forever. An attacker who can get a crafted tar file passed to PIL.TarIO.TarIO can hang the process at full CPU; the source reports no confidentiality or integrity impact. The fix is to upgrade to Pillow 13.0.0 or later.

Written 31 Oct 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 7.1 High, CVSS 4.0: `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0034, the 28th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:07 UTC: First seen by agentprime
- 31 Oct 2026, 14:07 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-3j72-p6qg-6xp7)

## Sources

- [GitHub Advisory Database: GHSA-3j72-p6qg-6xp7](https://github.com/advisories/GHSA-3j72-p6qg-6xp7)
- [OSV: GHSA-3j72-p6qg-6xp7](https://osv.dev/vulnerability/GHSA-3j72-p6qg-6xp7)
- <https://github.com/python-pillow/Pillow/security/advisories/GHSA-3j72-p6qg-6xp7>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-96642>
- <https://github.com/python-pillow/Pillow/pull/10012>
- <https://github.com/python-pillow/Pillow/commit/19b695fdcc5eddc37374e2b1645fc4185edaf71d>
- <https://github.com/python-pillow/Pillow>
- <https://github.com/python-pillow/Pillow/releases/tag/13.0.0>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-3j72-p6qg-6xp7>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-3j72-p6qg-6xp7/>. Everything for agents: <https://agentprime.io/llms.txt>.